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Chapter 3
Project Window
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instrumentA(3.2)
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To successfully structure the functions for your instrument, you must determine who will use
the instrument driver and how they will use the instrument. Define functions that stand alone
to perform a useful action. For example, it might at first seem logical to use the functions
SetDMMRange and SetDMMFunction for setting the range and function of a multimeter.
However, a more useful function might be ConfigureMeasurement, for setting up multiple
parameters.
Defining the Hierarchy of Functions
It is important to design the function hierarchy for the instrument driver carefully. When you
do, the user can identify the functions required by the desired action without the burden of
choosing from a long list of unrelated functions.
The concept of function classes is only apparent to the user from within the LabWindows/CVI
development environment. The application program calls all functions within an instrument
driver the same way, regardless of which function class they are in.
Defining the Function Parameters
To design the code for an instrument driver function, you must first establish its parameters.
Function parameters provide input information to the function and output variables where the
function can store its results. Output parameters often contain values that the function reads
from the instrument and formats for the user.
Data Types
You must define a data type for each parameter in each instrument driver function. All data
types the instrument driver uses must be intrinsic C data types or data types that you define in
the .h file and list in the .fp file. You specify the data type of a parameter when you create
its corresponding control on a function panel. This data type must also be consistent with the
function prototypes in the instrument driver header file.
LabWindows/CVI uses the data type information to implement the variable declaration and
run-time checking capabilities when users operate function panels. When you declare a
variable from a function panel, LabWindows/CVI presents options based on the data type you
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LabWindows/CVI User Manual